A first type of such a machine is used for making trenches in the ground to considerable depth, up to 100 meters (m), and of width that is relatively small compared with said depth, the width typically lying in the range 500 millimeters (mm) to 1500 mm. One of the advantages of such machines is to enable such deep trenches to be made while complying with a requirement for being accurately vertical. The trench as a whole is obtained by successively digging adjacent panels.
In general, such cutter machines are constituted by a box structure of considerable height that serves to provide mechanical guidance to the excavator machine as the trench is being made. At the bottom end of the box structure there is a cutter head. These machines are themselves well known and it therefore suffices to mention that the cutter head is usually constituted by two cutter motors each usually carrying a pair of drums on which cutter tools are mounted. Each pair of drums rotates about a common axis, with the two axes of the cutter motors being parallel and horizontal in use. The cutter drums are driven in rotation by hydraulic motors.
Various types of mount are possible.
In another configuration, made available in particular by the supplier Casagrande, the hydraulic motors are located in the bottom portion of the box structure of the machine above the cutter head, and power is transmitted to the cutter drum by a transmission chain.
European patent EP 0 262 050 in the name of Soletanche, discloses a method of driving cutter drums in which the single hydraulic motor is mounted inside the cutter drums and is connected thereto by a stage of reduction gearing, or else by direct transmission. Power is delivered in hydraulic form via ducts connected to the cutter motor.
A second type of such a machine is used for making diaphragm walls molded in the ground that are obtained by cutting a trench in the ground having the shape of the wall that is to be made and by in-situ mixing the cut ground with a hydraulic binder. This technique of making diaphragm walls is known as “soil mixing”.
The diaphragm wall is generally not as deep as the above-mentioned trenches. In addition, in order to enable the cutter head to be extracted from the mixture of cut ground and hydraulic binder, the box structure of the machine is of dimensions that are much smaller. Nevertheless, the cutter head of such soil mixing machines is also usually constituted by two cutter motors each carrying a pair of cutter drums.
For this type of machine, the solution adopted in particular by the supplier Bauer, has the hydraulic motor placed on the box structure above the cutter head. Power is transmitted via a small diameter shaft that is substantially vertical and that passes through the thickness of the plate forming the bearing for the cutter motor. The cylindrical shaft engages a pair of bevel gearwheels that take off motion on a horizontal axis. A system of epicyclic gearing reduces the speed of rotation and increases the torque so as to drive the cutter drum effectively.
The first and third embodiments of the ground cutter machine present the major drawback of having hydraulic motors above the cutter head and thus of mounting those motors in a manner that is more complex and more expensive. In particular, it is not possible to change the cutter heads quickly.
Furthermore, the elements of the drive transmission system for the first and third embodiments (gearing, speed reduction, chain) leads to relatively high losses, of the order of 15%, that do not occur in the configuration described in the European patent in the name of Soletanche.
In addition, when each cutter motor drives two cutter drums, it is important that different conditions in terms of the resistance to rotation of the drums due to lack of uniformity in the ground encountered by the machine should not lead to any damaging effect on the strength of the cutter motors.